"The militants have cordoned off the area. So far they've retrieved 11 bodies from the debris," a second security official said.

"The death toll may rise because the militants are still searching for bodies."

Identities unclear

Al Jazeera's Kamal Hyder, reporting from the capital, Islamabad, said the attack lasted for up 20-25 minutes.

"According to reports from the area, up to 18 missiles were fired against targets on the ground. These were encampments and vehicles."

in depth

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There was no word on the identity of any of the fighters killed but the attack was in an area where members of an Afghan Taliban faction led by a commander known as Gul Bahadur operate.

Foreign fighters linked to al-Qaeda are said to be in the area as well as Pakistani Taliban fighters fleeing an army offensive in South Waziristan.

Drone attacks have stirred anger in Pakistan as they often result in civilian casualties.

According to statistics compiled by Pakistani authorities, more than 90 per cent of the 708 people killed in attacks targeting the tribal areas in 2009 were civilians.

Mosharraf Zaidi, a journalist in Islamabad, said the killings of innocent people were feeding into "the radicalisation agenda and narrative that many people in Pakistan are subject to."

"If the only metric of success is to kill members of al-Qaeda and the Taliban, then certainly [drone attacks] have been successful," he told Al Jazeera.

"But if the objective is to win the global war on terror and to defeat the radicalisation agenda in this part of the world, and ensure that we're not creating new terrorists and new recruits for al-Qaeda and the Taliban, then ... I think there are a lot of questions."

Attacks to expand

Last week, officials said that the US intelligence agency had been granted approval by the government to expand drone strikes in Pakistan's tribal regions in a move to step up military operations against Taliban and al-Qaeda fighters.

Targets would now include low-level combatants, even if their identities were not known.

Last month, Hakimullah Mehsud, the leader of the Pakistani Taliban who was previously thought killed by a missile from a drone, appeared in internet videos threatening suicide attacks in the US.

Hillary Clinton, the US secretary of state, said Washington expects more co-operation from Pakistan in fighting terrorism and warned of "severe consequences" if an attack on US soil were traced back to the country. 

Faisal Shahzad, the suspect in the Times Square bombingattempt, has reportedly claimed to have visited a Taliban camp in the Waziristan region.

CIA-operated drones have frequently targeted the group over the past year, and its members have vowed to avenge strikes that have killed several of their commanders.

Shah Mehmood Qureshi, Pakistan's foreign minister, told CBS television channel last week that the US should not be surprised if fighters try to carry out more attacks.

"They're not going to sort of sit and welcome you [to] sort of eliminate them. They're going to fight back," Qureshi said.